Synthetic elastic and elastomeric products



Patented Sept. ,7, 1948 2,448,556 SYNTHETIC ams'nc AND emsrommuo PRODUCT 'Murray M. Sprung, Scotia, and Charles A. Burkhard, Alplaus, N. Y., assignors to General Electric Company, a corporation of New York No Drawing. Application January 16, 1947,

1 a Serial No. 722,459

13 Claims. (01. 26046.5)

This invention is concerned with novel synthetic elastic and elastomeric products and methods of preparing the same. More particularly, this invention relates to synthetic elastic products containing an elastic element thereof an elastic polymer of a methyland hydrogen-substituted polysiloxane wherein the methyl radical and the hydrogen are present in the form of recurring structural units corresponding to theformulas (CHa)2SlO andCHsHSiO.

In Agens application Serial No. 526,473, filed March 14, 1944, and assigned to the same assignee as the present invention, there is disclosed and claimed synthetic compositions comprising an elastic polymer of a dimethyl silicone in which substantially all the silicon atoms are each connected to two methyl groups, i. e., the condensation products of the claimed invention contain an average of approximately two methyl groups per silicon atom. These polymeric materials, which exhibit all the physical characteristics of lrnown natural and synthetic rubbers or elastic gums, for instance, elasticity, compressibility,

good tensile strength, etc., possess, in addition to the foregoing properties, additional properties unobtainable with prior rubbers orelastomers prepared synthetically or derived from natural sources. 1

For example, the products disclosed and claimed in the aforementioned Agens application can be elongated and stretched in the same manner as- Moreover, under the influence of heat and pressure, and in the presence of certain catalysts or vulcanization accelerators, the filled (or unfilled) elastic product may be converted to the infusible and insoluble state. More specific directions for the preparation of these synthetic elastic products and the synthetic elastomerlcs compositions therefrom, i. e., the vulcanized products, as well as the properties and structural constitution of these polymeric organo-siloxanes, may be found in the previously mentioned Agens application 2 and in the applications of Marsden and Roedel, Serial No. 598,913, filed June 11, 1945, and Serial No. 549,128, filed August 11, 1944, now Patent No. 2,346,220, in Marsden application Serial No. 676,105, filed June 11, 1946, and in Sprung application Serial No. 676,091, flied June 11, 1946, all the foregoing applications having been assigned to the same assignee as the instant application.

One of the difilculties encountered in the manufacture of synthetic elastomers i. e., the heatconverted orvulcanized products obtained from the elastic gums, has been th-eexcessive lengths of time required to heafitreat the molded product prepared therefrom in order to efiect complete cure or conversion of the molded object to the infusible or insoluble state. For example, in the preparation of dimethyl silicone elastomers from elastic compositions obtained as a result of elfecting conversion to the elastic gum stage of the hydrolysis product I of dlmethyl dichlorosllane (see the aforementioned Agens application), it is often necessary to heat the molded product for from about 10 to 25 hours at elevated temperatures of the Order of approximately 200 C. to completely sure the molded product. This extensive heating cycle is necessary due to the extremely slow curing properties of the elastic coznposition, notwithstanding the incorporation of cure accelerators.

We have now discovered that heat-curable synthetic elastic products containing as an elastic element thereof an elastic, polymeric organesiloxane comprised substantially of the recurring structural units corresponding to the formulas crm=s1o and CI-IaI-ISiO (or stated alternatively, the recurring structural units may be shown as which units, with regards to their occurrence, may be presentln a regular or random distribution) can be cured or rendered infusible and insoluble in much shorter periods of time than has In addition to the faster cure described above, other advantages accruing from the practice of our invention are more rapid conversion of the liquid oily hydrolysis product at room temperature to the elastic gum stage with ordinary elasticizing agents, curability of the elastic products at lower temperatures, curability at higher temperatures within shorter periods of time, relatively high tensllestrengths of the elastomeric compositions prepared from these elastic polymeric materials, especially inthe absence of certain reinforcing fillers, increased hardness, etc.

The synthetic elastic products with which our invention is concerned, and which may be employed in the preparation of the synthetic elastomers, may be prepared in several ways. One method comprises hydrolyzing a mixture comprising (1) a pure or substantially pure dimethyl dihalogenosilane, for example, dimethyl dichloro silane, or an equivalent methyl-substituted silane, for instance, dimethyl diethoxy silane, or a silane containing two-methyl groups and two hydrolyzable groups connected to the silicon atom, and (2) a silane containing a methyl group and a hydrogen' connected to the silicon atom, the two other valences of the silicon atom being satisfled by two hydrolyzable groups, e. g., chlorines.

A more complete description of the nature of the methyland hydrogen-substituted polysiloxanes used in practicing the present invention may best be obtained by reference to their preparation. In the preparation of methyl halogenosilanes (methyl silicon halides) according tothe direct synthesis of that disclosed and claimed in Rochow Patent 2,380,995, issued August 3, 1945, and assigned to the same assignee as the present invention, for example, there is obtained a mixture of methyl halogenosilanes of the formula (CHJMSiXH wherein X is a, halogen atom and a is a number equal to l, 2, or 3. By fractional distillation, the different compounds may be isolated in a substantially pure state, the degree of purity depending on the nature of substituent X as'well as on the efficiency of the distillation apparatus. For example, in the fractional distillation of a methyl chlorosilane mixture, dimethyl dichlorosilane is obtained at a temperature of about 70 C. at 760 millimeters. As is the case in most distillation processes, the dimethyl dichlorosilane is not absolutely pure but ordinarily contains some methyl trichlorosilane which boils at about 66 C. For the purposes of the present invention, we can use a dimethyl dichlorosilane fraction containing less than 2 mol per cent of methyl trichlorosilane, the optimum upper range of the methyl trichlorosilane being less than 0.51 mol per cent.

The other halogenosilane, for example, methyl dichlorosilane (CI-IaSiI-IClz), which is employed in the preparation of our claimed elastic gums or compositions, is also obtained along with the aforementioned methyl halogenosilanes. However, since the methyl dichlorosilane boils at a much lower temperature than the other methyl chlorosilane mentioned previously (about 41 C.) no difficulty is encountered in removing the methyl dichlorosilane from the other methyl chlorosilanes.

In the preparation of the elastic polymers of the claimed methyland hydrogen-substitutedpolysiloxanes, the dimethyl dichlorosilane is pref erably cohydrolyzed with the methyl dichlorosilane. However, it is within the scope of this invention to hydrolyze the individual constitucats separately, and mix the resulting liquid oily hydrolysis products together. Thereafter, the hydrolysis product (whichever one is employed) is contacted with a minor proportion, preferably from approximately 0.5 to 5 per cent, by weight (based on the weight of the cohydrolysis product), of a condensation catalyst or elasticizing agent capable of converting the liquid oily hydrolysis product (or mixture of hydrolysis products) to the elastic gum stage. Among the elasticizing agents which may be employed for this purpose are ferric chloride, alkali-metal hydroxides, for example, sodium hydroxide, potassium hydroxide, etc.: sulfuric acid, phenyl phosphoryl chloride (CsHsOPOCh), dimethyl dichlorosilane, etc. We prefer to use phenyl phosphoryl chloride as the elasticizing agent, the use of such agent being more specifically disclosed and claimed in the aforementioned Sprung application (supra).

The transformation of the liquid oily hydrolysis products which contain an average of from about 1.98 to 2.0 total methyl radicals and hydrogen atoms per silicon atom to elastic gums (and thereafter toheat-converted synthetic elastomars) is believed to be due to a rearrangement of the repetitive units [(CHa) 2310 and CHaHSiO] .of the siloxane polymyers into polymers of extremely high molecular weight which may best be described as elastic gums or solids having springy or elastic recovery characteristics and being capable of recovering size and shape after deformation. This transformation may be accomplished in a number of ways, for instance, by

- the useof the elasticizing agents previously mentioned. The conversion of the liquid hydrolysis products to the elastic gum stage by the elasticizing agents may be effected under the influence of heat, for example, from above room temperature (25 C.) to about C. However, we prefer to incorporate the elasticizing agent in the liquid hydrolysisproduct and allow the mixture to stand at room temperatures for the varying lengths of time required to yield the above-described elastic gums or compositions.

In order to prepare synthetic elastomeric compositions from the elastic gum, the latter is.

worked on ordinary mixing or diilerential rolls used in milling rubber until it attains the desired consistency for molding or extruding. Curing catalysts or vulcanizing agents and fillers may be added during this operation. After being formed into the desired shape in molds under the influence of heat and pressure, the synthetic elastomers may be further cured or vulcanized,

by heat-treating in an oven until the desired degree oi cure is obtained.

In the case where, for example, dimethyl dichlorosilane and methyl dichlorosilane are cohydrolyzed together in the same hydrolysis medium, it is desirable, although not essential, that the molar proportions of the former to the latter be maintained within certain ranges. Thus, we have found that there is less difllculty in molding the elastic gum if the mixture of dimethyl dichlorosilane and methyl dichlorosilane contains at least 50 mol per cent of the former, preferably '10 mol per cent. Good results are obtained if, in the cohydrolysis step, the molar proportions of the aforementioned chlorosilanes comprise, by weight, from about 3 to 30 mol per cent methyl dichlorosilane and from approximately 97 to 70 mol per cent dimethyl dichlorosilane. If the amount of methyl dichlorosilane is substantially in excess oi-50 mol per cent, the elastomeric comconditions.

positions obtained therefrom cure to the infusible and insoluble state at such a rate that it is sometimes diiiicult to control the molding o! products therefrom. In addition, the heat-converted or vulcanized compositions obtained from elastic gums prepared from hydrolysis products containing more than 50 mol per cent of the structural unit CHaHSiO tend to be harder with lower tensile strengths.

In order that those skilled in the art may better understand how our claimed synthetic compositions may best be prepared, the following examples are given by way of illustration and not by way of limitation. All parts are by weight.

Exlmrtl: 1

' composition. About 100 parts of the above elastic gum was milled with approximately 200 parts titanium dioxide and 2.5 parts benzoyl peroxide, Several samples were molded from the filled ma terial by pressing them for about minutes at 150 C. under a pressure of about 1000 p. s. i. Thereafter, the samples were cured for varying the lengths of time at difierent temperatures to determine the eii'ect on tensile strength, elasticity, and hardness of the respective samples. The following table shows the results of curing the samples under the aforementioned varying.

linux32 'In this example. samples of synthetic elastomerlc compositions were prepared in the same manner as was done in Example 1 with the exception that the mixture of chlorosilanes employed at the beginning comprised, by weight. about 25 mol per cent methyl dichlorosiiane and 75 mol per cent dimethyl dichlorosilane. The elasticizing process, 1. e., the conversion of the liquid oily hydrolysis product to the elastic gum stage, and the compounding of the elastic gum with the same proportion of titanium dioxide and benzoyl peroxide were substantially the same as that employed in Example 1. Table 2 shows the results of heat-treating the samples for various periods of time at diflerent temperatures.

Table 2 Tensile Cure Time Hours 3?" g E ia 1512i Hii d r igss 2; 100 340 100 62 4... 100 370 100 1. 150 380 100 58 150 400 I00 63 e 150 440 v 100 67 200 570 7O EXAMPLE 3 The following results show the effect on the synthetic elastomeric compositions of using varying molar proportions of methyl dichlorosilane (in the preparation of the elastic gum) in combination with. the same filler, namely, titanium dioxide, with and without the presence of cure accelerators or vulcanizing agents, e. an, lead oxide or benzoyl peroxide. The mixture of dimethyl dichloros'ilane and methyldichlorosilane were cohydrolyzed and converted to the elastic gum Table 1 stage in the same manner as was done in Example t. In each case, about 200 parts tita- Tem Tensile Per Cent Show nium dioxide were milled with parts of the Cure Time, Hours tpr s Elongation Hardness particular elastic gum. The hydrolysis of the 45 mixture of chlorosilanes, conversion of the hy- 240 150 47 drolysis product to the elastic gum stage, and 150 329 100 compounding on differential rubber rolls and 53g 2 5% :33 gg molding of the filled material wereadentical with 200 425 100 the procedures employed in Example 1. All the 435 75 76 50 molded sheets were cured for-18 hours at 150 C. before physical properties were determined.

Table 3 Mol Per Hardness Sam l Cent Tensile Per Cent N p Methyl Cure Accelerator Strength, Elongation Hydrogen p. s. i. at Break Scleri- Sh Silicone Scope ore A 1. 5 Benzoyl Peroxide, 2.5 parts 565 66 B- 3.0 do 700 66 E- 6.0 46 D 6.0 Benzoyl peroxide, 1 part; Lead Monoxide, l pal-L.-- 380 60 E 6. 0 Benzoyl peroxide, 2 rts; Lead monoxide, 1 part..- 460 63 F. 6.0 Benzoyl peroxide, 2. parts 650 72 0.- 12.5 240 68 H i2. 5 Benzoyl peroxide, 2.5 parts 760 78 for at least 10 hours at 200 C. 75

It will be apparent to those skilled in the art that fillers other than those employed in the foregoing examples may be used. These include, e. g., ferric oxide, antimony oxide, asbestos in various forms, for example, asbestos floats, asbestos fibers, etc., comminuted glass fibers, whiting, lithopone, talc, zinc oxide, powdered silica, and the other finely divided solid materials used as fillers for natural and synthetic rubbers. Further information as to methods and procedures for hydrolyzing the chlorosilanes or mixtures of chlorosilanes, for converting the hydrolysis products to the elastic gum stage, and for compounding and molding the elastic filled or unfilled compositions may be found in the aforementioned Agens application.

The novel methyland hydrogen-substituted synthetic elastic polysiloxane compositions and synthetic elastomers prepared therefrom, as disclosed and claimed in our invention, are useful in applications where materials having rubberlike properties are required, such as gaskets, electrical insulation (for example, conductor insulation) shock absorbers, etc. Owing to their resistance to deterioration at high temperatures and their resistance to embrittlement at low temperatures, they are particularly useful in applications where natural rubbers or other synthetic rubbers fail, owing to the deleterious effect of heat or cold.

What we claim as new and desire to secure by Letters Patent of the United States is:

l. A solid, elastic, curable polysiloxane cnsisting of methy1 radicals, and hydrogen, silicon, and oxygen atoms obtained by condensing a liquid consisting of polymeric dimethylsiioxane containing (a) up to 2 mol per cent copolymerized monomethylsiloxane and (b) from 1.5 to 50 moi per cent copolymerized methylhydrogensiloxane.

2. A heat-curable, synthetic, elastic product comprising a filler and containing as the elastic element thereof a solid, elastic, curable polysiloxane consisting of methyl radicals, and hydrogen, silicon and oxygen atoms obtained by condensing a liquid consisting of polymeric dimethylsiloxane containing (a) up to 2 mol per cent copolymerized monomethylsiloxane and (b) from 1.5 to 50'mol per cent copolymerized methylhydrogensiloxane.

3. A synthetic, elastic product comprising the cured composition of claim 2.

4. A new composition of matter comprising essentially the solid, elastic, heat-curable product of reaction 6f ingredients including (1) a liquid consisting Of polymeric dimethylsiioxane containing (a) up to 2 mol per cent copolymerized monomethylsiloxane and (b) from 1.5 to 50 mol per cent copolymerized methylhydrogensiloxane and (2) a condensing agent for (l), the reaction between the condensing agent and the liquid polymer of (i) being allowed to take place for a time suflicient to yield the aforementioned solid, elastic product.

5. A new composition of matter comprising essentially the solid, elastic, heatcurable product of reaction of ingredients including (1) the liquid product of cohydrolysis of a mixture of ingredients consisting of dimethyldichlorosilane containing up to 2 mol per cent methyltrichlorosilane and from 1.5 to 50 mol per cent methyldichlorosilane and 2) a condensing agent for l) the reaction between the condensing agent and the aforesaid liquid cohydrolysis product of (1) being allowed to take place for a time sumcient to yield the aforementioned solid, elastic product.

6. A new composition of matter as in claim wherein the condensing agent is phenyl phosphoryl chloride. 1

7. A solid, elastic, heat-curable product obtained by treating with from 0.5 to 5 per cent,

8 by weight, oi a condensing agent, a liquid consisting of polymeric dimethylsiioxane containing (a) up to 2 moi per cent copolymerized monomethylsiloxane and (b) trom 3 to 30 mol per cent copolymerized methylhydrogensiloxane, the reaction between the condensing agent and the aforesaid liquid being allowed to take place for a time suilicient to yield a solid, elastic product.

8. The 'process oi making a new synthetic. solid, elastic, curable polysiloxane, which comprises treating, with a condensing agent, a liquid consisting of polymeric dimethylsiioxane containing (a) up to 2 mol per cent copolymerized monomethylsiloxane and (b) from 1.5 to 50 mol per cent methylhydrogensiloxane, the said liquid methyland hydrogen-substituted polysiloxane containing an average of from 1.98 to 2.0 total methyl groups and hydrogen atoms per silicon atom, the aforementioned liquid polymer being treated with the condensing agent for a time suificient to yield a solid, elastic product.

9. The process as in claim 8 wherein the condensing agent is phenyl phosphoryl chloride.

10. The process oi making a cured, synthetic, elastic composition which comprises, (1) treating with a condensing agent a liquid consisting of polymeric dimethylsiloxane containing (a) up to 2 mol per cent copolymerized monomethylsiloxane and (b) from 1.5 to 50 mol per cent copolymerized methylhydrogensiloxane thereby to obtain a solid, elastic, curable polysiloxane, (2) compounding the said material with a filler, and (3) advancing the cure of the filled material under the influence of heat.

11. The process as in claim 10 wherein the solid, elastic, heat-curable material is compounded with a cure accelerator consisting of benzoyl peroxide and a filler comprising titanium dioxide.

12. The process of making a heat-curable, solid, elastic composition which comprises 1) hydrolyzing a mixture of halogenosilanes consisting of (a) from 50 to 97 mol per cent of dimethyldi halogenosilane, (b) from 0 to 2 mol per cent of a methyltrihalogenosilane, and (c) from 3 to 50 mol per cent of a methyldihalogenosilane. and 2) treating the resulting oily, isolated hydrolysis product with a condensing agent for a length of time sufllcient to yield a solid, elastic, heat-curable product.

I l 13. The process which comprises (1) hydrolyzranging from about 25 C. to 125 C. for a time REFERENCES CITED The following references are of record in the tile of this patent:

UNITED STATES PATENTS Number Name Date 2,377,689 Hyde June 5, 1946 2,392,713 Wright et al. Jan. 8, 1946 Certificate of Correction Patent No. 2,448,556. September 7, 1948.

MURRAY M. SPRUN G ET AL. It is hereby certified that errors appear in the printed specification of the above numbered patent requiring correction as follows:

Column 2, line 4, for the patent number 2,346,220 read 2,486,220; line 38, for that portion of the structural unit reading Si-C reed --S1l-O;

and that the said Letters Patent should be read with .these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 1st day of March, A. D. 1949.

THOMAS F. MURPHY, 1

Assistant Commissioner of Patents. 

